Photo-electric apparatus



W. 0. SNELLING.

PHOTO-ELECTRIC APPARATUS.

APPLICATION r1150 JULY 9. 1920.

1,375,474. Patented Apr. 19,1921.

Fig.1

or wire gauze.

UNITED STATES WALTER O. SNELLING, OF ALLEN'IOWN, PENNSYLVANIA.

PHOTO-ELECTRIC APPARATUS.

' Specification of Letters Patent.

Patented Apr. 19, 1921.

Application filed July 9, 1920. Serial No. 395,082.

To all whom it may concern.-

Be it known that I, WALTER O. SNELL NG, a citizen of the United States, residing at Allentown, in the county of Lehigh and State of Pennsylvania, have invented certain Improvements in Photo-Electric'Apparatus, of which the following is a specification.

My invention relates to improvements in electrical apparatus, and more particularly relates to an lmproved photo-electric cell.

It has long been known that selenium, particularly when in the form known as metallic selenium, undergoes a remarkable change in electrical resistance under the influence of actinic rays. In the absence of light the electrical resistance of selenium is relatively high, but in the presence of actinic rays the electrical resistance is greatly re duced, this property enabling selenium to be employed as a sensitive means for detecting and even measuring actinic radiation.

It has also been known for some time that light-sensitive selenium cells are themselves capable of generating electrical energy, when actinic ra s fall upon them.

One of the o jects of my present invention is to produce a photo-electric cell of relatively cheap construction and high actinic efiiciency, and for the purpose of better explaining the underlying principles of my new cell I have shown in the accompanying drawing two forms of cell which embody the features of my invention, but 1 do not limit myselfto the form of cell shown in the drawing, since the principles of my invention may be broadly applied to many other types of photo-electric devices.

In the drawing Figure 1 shows a cross-section through a very simple form of cell, while Fig. 2 shows a cross-section through a modified cell of more rugged construction. In both of these figures 1 represents a plate of some conducting metal, such as copper for example, 2 represents a layer of a photoelectric material such as metallic selenium, 3 represents an aqueous electrolyte, such as a concentrated salt solution, and 4 represents a metallic electrode, such as stretched wires In Fig. 2, 4*" represents a secondary metallic electrode of wires or wire gauze, 5 represents gaskets of rubber or other suitable insulating material, 6 represents a protecting plate of glass or other transparent covering material and 7 represents clamps for suitably holding the other elements of the apparatus in proper position. 8, 8 and 8 represent wires for attaching the photo-electric cell to other electric apparatus. These elements are shown diagrammatically only, and no attempt has been made to show the relative thickness'of the layers of selenium or aqueous electrolyte; but preferably both of these should be very thin to insure minimum electrical resistance. The arrows in the drawing indicate light rays. Flg. 3 is a perspective view of a cell of the kind shown in section in F ig; 2, for the purpose of better showing the relationship of the clamp 7 to the other parts of the apparatus.

In the construction of my improved photoelectric cell I first prepare a thin film of a photo-sensitive material upon a material which is a good conductor of electricity.

VThis may be eflf'ected by any of the wellknown methods, a satisfactory method being the spreading of finely divided selenium evenly over a plate of copper, and then covering this layer of selenium with a flat plate of glass, mica, or other material, and simultaneously heating the copper plate and pressing the selenium layer. The selenium melts and forms a thin, smooth and firmlyadhering film. If glass is used, care must be taken in this operationto cool the glass surface at the'same time that the copper plate is being heated, as selenium tends to adhere firmly to glass when it is heated in con tact with it for some time. t

Having obtainedin the manner described, or in any other convenient way, a suitable layer of a photo-electric material on a good electrical conductor, I next prepare a transparent electrode in contactwith the photosensitive film, this constituting the essential element of my invention. In Fig. 1 this transparent electrode is a thin film of gelatin or starch paste, and in Fig. 2 this transparent electrode is an aqueous salt solution. Even when I use as my transparent electrode a colloidal jelly of starch paste, gelatin or other similar material, I find it of advantage to have an electrolyte such as dilute acid or a solution of ionizin salts present. Since even such colloidal jellies possessrelatively high electrical resistance, I find it of advantage to have such films as thin as possible, and I place in or over such films transparent gauze of wire of high electrical conductivity.

From the foregoing description it will be evident that the essential feature of my invention is an electrically conducting and light-transparent electrode in contact with an electrically-conducting and light-transparent aqueous fluid or colloidal jelly, this latter material being in turn in contact with a photo-electric surface of selenium or like material, and this surface of selenium or other photo-sensitive material being in firm electrical and mechanical contact with a plate of metal, which serves as one electrode of the cell.

Many efforts have hitherto been made to make photo-electric cells of low electrical resistance and high electrical sensitiveness. The most successful of such cells has been the Fritts cell, in which one electrode consists of a thin layer of selenium spread over one surface of a metal plate, while the other electrode consists of a thin sheet of metal foil in contact with the selenium surface. My present photo-electric cell may be considered as a modification and improvement of the F ritts cell, and I have discovered that by replacing the translucent gold foil electrode by an electrode comprising an aqueous solution of high electrical conductivity, the photo-electric efficiency of the cell is greatly increased.

It is evident that a wide range of equivalents may be employed, without departing from the spirit of my invention. Instead of employing a transparent electrode of starch paste or gelatin, I may use an electrode of agar jelly, chondrus jelly, silica jelly, or other similar materials. Instead of employing a gauze net-work in or on my transparent aqueous electrode I may employ a grid of wires arranged in parallel position. Where I use two electrically insulated sets of electrodes, as 8" and 8 in Fig. 2, either or both of these may be composed of wire gauze, the purpose of employing two sets of electrodes being to indicate and utilize photo-electric differences of potential existing between these two sets of grids. The purpose of the cover 6, of glass or other transparent material, is to serve as a protection to the transparent aqueous electrolyte, and to reduce the evaporation of same. Where a cell is used in a horizontal position, a thin layer of oil may replace this protecting glass surface to advantage, particularly in the case of photo-electric cells of large size, The light should preferably fall upon the cell in a direction perpendicular to the.

plane of the photo-electric film, the maxmum efficiency being thus obtained. Where 'it is desired to have photo-electric cells which are more sensitive to certain forms of radiation than to others, .as for example, cells which are more sensitive to rays of yellow light than to rays of green light, this result can be conveniently obtained by adding a suitable dye to the electrolyte 3,

the sensitiveness of the cell to selected colors being greatly influenced in this way.

I find it desirable in the construction of my conducting grids to'use wire of high electrical conductivity, since in this way I obtain minimum electrical resistance and maximum transmission of light through my aqueous electrode to the photo-electric surface. Although as mentioned I prefer to employ wire in the form of wire gauze, the

use of gauze is not necessary, and wires stretched in parallel position maybe employed instead, the function of the wires being to assist the electrical conductivity of the aqueous electrolyte.

The essential element of my invention is the employing of an aqueous solution or a colloidal jelly as one electrode of a photoelectric cell, in conjunction with a grid of wire or Wire gauze in or on such electrode, the aqueous electrode being in contact with a film of photo-electric material serving as 2. A transparent electrode for photoelectric cells comprising a grid of wire in contactwith an aqueous colloidal jelly.

3. A transparent electrode for photoelectric cells comprising a sheet of wire gauge in contact with a sheet of an aqueous fiui 4. A photo-electric cell comprising a film of a photo-electric material in contact with a film of an aqueous fluid containing an electrode in the form of a wire grid.

5. A photo-electric cell comprising a metallic electrode, a fihn of a photo-electric material in contact with such electrode, a thin layer of an aqueous fluid in contact with such photo-electric film, and a wire grid in contact with such aqueous fluid.

6. A photoelectric cell comprising a metallic electrode, a film of a photo-electric material in contact with such electrode, a thin layer of an aqueous fluid in contact with such photo-electric film, a wire grid in contact with such aqueous fluid, and a layer of transparent material over the layer the film of aqueous electrolyte and the film of aqueous fluid to reduce the evaporation of photo-electric material having a surface of such fluid. of contact. 10 7. A photo-electric cell comprising a plate In testimony whereof, I have hereunto 5 of metal in contact With a film of photosubscribed my name this 2nd day of June,

electric material and a grid of Wire in con- 1920. tact with a film of an aqueous electrolyte, WALTER O. SNELLING. 

